anv/device: Handle non-4k-aligned calls to MapMemory

anv/device: Handle non-4k-aligned calls to MapMemory

As per the spec:

   minMemoryMapAlignment is the minimum required alignment, in bytes, of
   host-visible memory allocations within the host address space. When
   mapping a memory allocation with vkMapMemory, subtracting offset bytes
   from the returned pointer will always produce a multiple of the value of
   this limit.